Do you feel it's more common for siblings to grow apart as we go through life... or more unusual?

There's tons of varying dynamics that enter in this, obviously.. and the fact that many brothers and sisters are geographically distanced is just one.
I've been fretting for a couple of weeks over a simmering conflict between my son and daughter. It seems to have blown over now, thank goodness, but really illustrated to me the widening gap in their relationship..which could best be described as cordial, but cool and detached.

Indifferent might be the word.
If not for family dinners and outings where my husband and I are joining, they'd never see or talk to each other, I'm sure. ( live 10 miles apart)
They've never been really close, didnt get along as children and teens, though each got along well with their younger brother throughout his too-short life.

They're both warm and loving with us, and with their respective families.
As a mother,I've always been bothered and disapointed that they dont have a better relationship.. and puzzled as to why they dont.
But I have to accept that only they can fix that. It's not about conflicts - that's part of family life. It's about the bonds.
I'm just left wondering sometimes.. where is the love between these two?

Guess it's there,deep down. Hope so.

Clearly no family is "The Brady Bunch".

And if we have more than one sibling.. each relationship is going to be different, naturally.
My husband says siblings usually slowly drift apart as years go by.. kind of a natural progression in life...and our children's relationship is not "that" unusual.
I do agree to a certain point, but when I look around, I see lots of examples of brother and sister closeness that lasts a lifetime too.
Not all of you have siblings and/ or children of course, but wondered what your thoughts were on this topic, or, if you care to share... your own family experiences